I run Orks, and I was never really impressed with grots. They're the same idea, except Cultists are a tad bit tougher. I ran into the same problem every time I ran them: It would take a single small unit to walk right through and take their objective. Going to ground is great, and it could save them for a few turns, but they aren't fearless. I'd probably only take them in the minimum squad size, so I can only lose 3 before they have to take a Ld test. Or a small assault unit could destroy them in one turn. I'm not too enthusiastic about Cultists.
As for anti-air, I might try out those havocs. Can getting dakka helbrutes do anything about it? And for Vehicles in general, do Dakka Brutes sound better than close combat Brutes?
That's so ridiculous that a Champion of freaking Noise Marines cannot take a sonic blaster or a blastmaster. That's completely ridiculous.